[x264-devel] Re: Rate control in x264

[Loren Merritt]

On Mon, 21 May 2007, Son Minh Tran wrote:

> I try some tests on the performance of CABAC. Then I need exactly the same 
> input data for CABAC encoder. Because of the rate control of x264, I do think 
> that I don't have the same quantized data (before CABAC encoding phrase) 
> of the frame T if in the previous frames, the output of the whole coder
> (after CABAC encoding phrase) was different.
> I know that there are 5 models of rate control in x264. What I need is the 
> constant quantizer. Would you please show me how I can activate this mode? Is 
> it enough to use --qp N at the command line?

Yes. And crf mode also works in that it doesn't take any feedback from
the actual size of the encoded pictures, so its choices will be
independent of the entropy coder.
But ratecontrol isn't the only way the entropy coder can influence
encoding decisions. Also make sure not to enable rate-distortion
optimization or trellis.

--Loren Merritt

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